Vacuum tube



Patented Oct 29, 1929 UNITED STATES PATENT OFFICE WILLIAM A,.MACDONALD,OF LITTLE NECK, NEW YORK, ASSIGNOR TO HAZELTINE CORPORATION, OF JERSEYCITY, NEW JERSEY, A CORPORATION OF DELAWARE VACUUM TUBE Applicationflled July 10,

This invention relates to vacuum tubes, more particularly to thestructure of thermi onic vacuum tubes having two or more lnternalelements or electrodes, and has for its object the provision ofstructural features which effect extreme rigidity of the elements,economy in manufacture, and certain other improvements hereinafter to bedescribed.

The rigidity of the elements of vacuum tubes has become of increasingimportance as the various apparatus to be used therewith have beendeveloped to be more efficient and critical. For many reasons a longcathode element or filament electrode is desirable, and there has beenespecial dilficulty in supporting this element so that it will not sagor change its position relative to the other elements. It has been thepractice to utilize a glass press for supporting the individual elementsthrough the medium of a number of supporting wires which may besuitablybent to align and space the elements. These wires, after passing througha glass press, are likewise employed to make external connections totheelements of the tube. After the tube is assembled, a mechanical shockor blow will often bend the supporting wires and materially change thetube characteristics, or even bring the elements into electricalcontact. Such means of element support also allows of objectionablevibration of the elements which results in what is commonly calledmicrophonic action.

With a view toward increased rigidity, it has been suggested to clampthe plate electrode securely to the glass stem below the press, and tolocate and space the grid and filament electrodes by means of insulatingblocks attached to the extremities of the plate. This method appears toprovide more rigidity than the former method, but is not so generallyused because of greater manufacturing cost. In addition, it will benoted that neither method provides any means for supporting the filamentrigidly throughout its length. The present invention I provides simplemeans for rigidly supporting the filament and concurrently providesmeans for supportingand spacing the other elements wlthin small 1925.Serial No. 42,757.

Fig. 2 illustrates two electrode-spacing caps secured in place on thefilament-supporting mandrel;

Fig. 3 isan end view of the assembly of .Fig. 2;

Fig. 4 shows the completely assembled electrode unit;

of Fig. 4 as supported above the press of a vacuum tube;

Fig. 6 is a front view of a complete vacuum tube including the elementsassembled, mounted and supported according to the invention; and a \vFig. 7 is a cross-section of an alternative form of mandrel.

Referring now to Fig. 1, it will be seen that a filament electrode orcathode element 1 is wound in a helix around a mandrel of refractorymaterial such as soapstone or Pyrex glass. The filament, whichfrequently is long and fragile, is thus supported throughout its entirelength byv the mandrel. According to a preferred construction, themandrel extends a short distance at each end beyondthe filament so thatelectrode-spacing caps 4 maybe secured over the end of the mandrel, asindicated in Figs. 1 and 2. A wire 3, larger and stronger than thefilament and which may Fig. 5 shows the completely assembled unitpreferably be of nickel, is molded or otherwise inserted into themandrel at each end thereof, and serves both to connect the filament tothe external circuit and to support the electrode assembly. In a vacuumtube of small size, one such wire in each end of the mandrel willusually prove sufficient; although if the completed assembly be somewhatheavier, a larger wire than shown, or

, low electrical resistance, and consequently a considerable length offilament wire must be employed in order that the filament may be heatedby an electric source at conveniently high potential and with aneconomically low current. In addition, platinum is to a large extentchemically inert, and may be successfully coated with electron-emittingsubstances.

-An enlarged cross-section of an alternative supporting mandrel is shownin Fig. 2. It is not always desirable to employ a supporting mandrelwhich touches the filament throughout its length, and therefore a flutedmandrel or one of polygonal cross-section,

. having a number of projections or edges which support the filamentsubstantially by point contact so that the heat from the filament willnot be conducted'away through the solid material of the mandrel, may bedesirable. It should be noted, however, that a mandrel of circularcross-section, as shown in Figs. 1 and 1, need not necessarily conductaway as much heat from the filament as would at first be supposed,because it is customary to coat the filament with an earthmetal oxide orother electron-emitting material to increase the natural electronemission of the cathode, and this oxide, or other coating, usuallypossesses the property of low heat conduction. If this substance doesnot possess that property, then a coating of'a substance which doespossess low heat conductivity may be applied to the mandrel. It has beenfound expedient first to coat the mandrel with such oxide or othersubstance, subsequently to wind the filament thereon, and then to applymore coating material to the filament and mandrel, thus embedding thefilament in an oxide or other coating.

The third step in the process of assembly would normally be'to mount thespacing or end caps 4 over the ends of the mandrel as shown in Fig. '2.These caps may be of a refractory and insulating material similar tothat used in the mandrel, or may be of a different material, but shouldbe formed accurately, because it is the dimensions of these 1 caps whichdetermine the spacing of the electrodes. It is usually preferable tomanufacture the spacing caps separately from the mandrel in order thatthe. dimenslons may be accurately determined, although, of course, if

the tubes are to be manufactured in large,

quantit utilized to form the mandrel and spacing caps in one integralpiece. During such molding process the comparatively low resistancelead-in wire 3 may also be molded in place.

-If the latter molding process is employed, the next operation ofassembly would be the placing of a grid electrode 8 upon shoulders 6(Fig.2) of the end spacing caps as indicated in Fig. 4. This electrodemay be of wire mesh, perforated metal, or of other suitableconstruction. If the grid electrode be 4 made in tubular form, it would,of course, be necessary to place it over the mandrel before the secondend cap is put in place. A slot 10 is shown in Fig. 3 through which isbrought the lead-in wire connected to the grid. The last operation inthe electrode assembly is the placing of the plate electrode or anode 9(Fig. 4) over the outer shoulders 7 of the spacing caps.

In the embodiment illustrated the plate electrode is of circularcross-section. It should be noted, however, that while, for conveniencein manufacture, electrodes of circular cross-section are desirable,electrodes of other cross-section, such, for instance, as that shown inFig. 7, may be utilized to advantage. I

In Fig. 5 the completed electrode assembly a molding process may readilybe,

is shown mounted and supported above the glass press 12, through whichthe connecting leads pass. Rigid supporting wires 11, which may alsocarry the filament current, are

shown extending from each end of the elec-.

trode assembly and are preferably spot-welded to the filament lead-inwires 3. It is in many instances desirable to make lead-in wires 3 of alen th and rigidity suflicient totake the place of supporting wires 11,and to anchor the same directly in the glass press 12.

The illustrations of the embodiment described show the elect-rodeassembly as being mounted horizontally in the glass envelope or bulb 13,Fig. 6; but, because of the unusually stable characteristics aiforded bythis invention, the assembly may be mounted vertically,

or in any convenient position, since the operating efiiciency is in noway influenced thereby. In order to conserve space and to expediteevacuation, the assembly illustrated "III in Fig. 4 may conveniently bemounted in a glass tube slightly larger than the diameter of plate 9,and two lead wires brought out from each end, thus eliminatng the largebase 14 shown in Fig. 6,'together with the increased effectiveinter-electrode capacity resulting therefrom.

The construction as illustrated and described above permits of veryrapid assembly by comparatively unskilled labor with the assurance of astandardized product of unvarying characteristics. As will at once beobserved, the plate-grid spacing isdependent entirely upon thedimensions of the spacsively by said end caps,

ing caps 4, which may be cheaply manufactured with great accuracy. heelectrode assembly is in itself extremely rigid, and is not affected inany way by vibration or mechanical shocks within reasonable limits. Thisrigidity is due to the unusually solid support of the variouselectrodes, by reason of the fact that the filament is su portedthroughout its entire length, and tiie grid and plate electrodes aresupported on both ends around their entire perlmeters. The assemblybeing in one complete unit, any shocks to WhlCh it may be subjected willaffect all of the electrodes simultaneously, and there will besubstantially no movement of any one electrode relative to the others.

I claim:

1. A vacuum tube electrode structure comprising a mandrel of refractoryinsulating material, a cathode comprising1 a filament supportedsubstantially throu out its entire length by said mandrel, oubleshoulders of insulating material at each end of said mandrel, a controlelectrode su ported at both ends by a pair of said shoul ers, an anodesupported at both ends by the other pair of saidshoulders, and meanspartially embedded in said mandrel for supporting said structure fromboth ends thereof within an evacuated envelope.

2. A vacuum tube assembly including a cathode structure which comprisesa man rel of insulating material coated with an electron-emittingsubstance, a filament coiled around said mandrel, and an additionalcoating of said electron-emitting substance embedding said filament, endcaps for said mandrel having spacing shoulders thereon, a tubularcontrol electrode supported and spaced from said filament electrodeexclua tubular plate electrode supported and spaced from said controlelectrode exclusively by said end caps, means for making externaconnections to said electrodes, and means including at least part ofsaid connecting means for supportin the electrode assembly within anevacuate envelope.

3. A vacuum tube comprising an elongated mandrel of refractorynon-conducting material, a filament wound helically around said mandreland rigidly supported thereby for substantially its entire length, apair of caps of refractory non-conducting material attache'd to oppositeends of said mandrel, each of said caps having a pair of shoulders, acylindrical control-electrode element supported at its ends by saidcaps, each end of said-=control electrode element being properlypositioned by one of the shoulders on its supporting cap, a cylindricalanode element supported at its ends by said caps, each end of said anodeelement being properly positioned by the other shoulder on itssupporting cap, said mandrel, caps, filament,

' ported control-electrode element and anode element being combined intoa unitary self-contained structure, said self-contained structure beingsupported exclusively by means connected to the ends of said mandrel,said filament, control-electrode element and anode element beingseparated except at their ends by evacuated space, and an evacuatedenvelope enclosirig said unitary structure.

4. vacuum tube comprising an elongated mandrel of refractorynon-conducting material, a filament wound helically around said mandreland embedded in a coating of electron-emitting oxide, said filamentbeing rigidly secured to said mandrel for substantially its entirelength by means of said oxide coating, a pair of annular caps ofrefractory non-conducting material attached to opposite ends of saidmandrel, each of said caps having a pair of concentric circularshoulders, a cylindrical control-electrode element supat its ends bysaid caps and enveloping said filament, each end of saidcontrolelectrode element being properly positioned by one of theshoulders on its supporting cap, a cylindrical anode element supportedat its ends by said caps and enveloping said control-electrode element,each end of said anode element being properly positioned by the othershouler on its supporting cap, said mandrel, caps, filament,control-electrode and anode element being combined into a unitaryself-contained structure, said unitary structure being supportedexclusively by means connected to the ends of said mandrel, saidfilament, control-electrode element and anode element bein separatedexcept at their ends by evacuate space, and an ev'acuated envelopeenclosing said unitary structure.

5. A vacuum tube assembly including a cathode structure comprising amandrel of refractory insulating material coated with a substance of lowspecific heat conduction, a heating filament wound around said mandreland su ported substantially throughout its entire ength thereby, anelectron emitting substance coating said filament, double shoulders ofinsulating material at both ends of said mandrel, a control electrodesupported at both ends by a pair of said shoulders, an anode supportedat both ends by the other pair of said'shoulders,

edded in said mandrel for supporting said structure from both endsthereof within evacuated envelope, and means for cdnd cting a heatingcurrent to and from said filament.

In testimony whereof I aflix my signature.

WILLIAM A. MACDONALD.

means partially im-

